1. Field of the Invention
The present invention relates, in general, to a method of fabricating a multilayer printed circuit board, and particularly, to a method of fabricating a multilayer printed circuit board, in which a circuit pattern can be formed in an insulating layer to thus decrease the thickness of a printed circuit board and realize a micro circuit, and a printed circuit board can be stably fabricated regardless of changes in temperature or humidity in the process of fabricating a printed circuit board.
2. Description of the Related Art
Generally, a printed circuit board (PCB), which is a circuit substrate playing a role in electrically connecting or mechanically holding predetermined electronic components, is composed of an insulating layer, made of phenol resin or epoxy resin, and a copper foil layer having a predetermined wiring pattern attached to the insulating layer.
The PCB is largely classified into, depending on the number of layers, single-sided PCBs, in which a wiring pattern is formed on only one surface of an insulating layer, double-sided PCBs, in which a wiring pattern is formed on both surfaces of an insulating layer, and multilayer PCBs, in which a wiring pattern is formed into a plurality of layers.
Among the types of PCB, the multilayer PCB is fabricated by impregnating a woven glass cloth with BT, FR-4, or another resin to thus prepare a core, laminating copper foils on both surfaces of the core to form inner circuits, and then conducting a subtractive process or a semi-additive process.
The method of fabricating the multilayer PCB using a subtractive process or a semi-additive process is described below.
In the method of fabricating the PCB according to a conventional technique, first, a copper clad laminate (CCL), in which copper foils are laminated on both surfaces of a first insulating layer, is prepared, and then a dry film is applied on the copper foils.
Next, the portion of the dry film other than the portion of the dry film corresponding to a circuit pattern is removed through exposure and development, after which the copper foil is etched using an etchant, thus forming an inner circuit pattern.
After the formation of the inner circuit pattern, the dry film, applied on the inner circuit pattern, is removed.
Next, a second insulating layer is formed on the inner circuit pattern, and then a via hole is formed through drilling.
After the formation of the via hole, a copper plating layer is formed on the inner wall of the via hole and the second insulating layer through electroless copper plating and copper electroplating, and then a dry film is applied on the copper plating layer.
Next, the portion of the dry film other than the portion of the dry film corresponding to an outer circuit pattern is removed through exposure and development, and then the copper plating layer is etched using an etchant, thus forming an outer circuit pattern.
After the formation of the outer circuit pattern, a third insulating layer is formed on the outer circuit pattern, and then a blind via hole is formed using a laser drill to expose the portion of the outer circuit pattern.
Next, a copper plating layer is formed on the inner wall of the blind via hole and the third insulating layer through electroless copper plating and copper electroplating, a dry film is applied on the copper plating layer, and then the portion of the dry film other than the portion of the dry film corresponding to an outermost circuit pattern is removed through exposure and development.
Next, the copper foil, exposed by removing the portion of the dry film, is etched using an etchant, thus forming an outermost circuit pattern.